DAC Offset Compensation for Accurate CMOS ADC References
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Solution Overview
Problem
Offset voltages introduced by component variations during non-ideal manufacturing processes affect the accuracy and linearity of analog-to-digital converters (ADCs), particularly in CMOS processes, where large net offset voltages can shift reference voltages and compromise ADC operation.
Innovation Solution
An offset compensation scheme using a digital-to-analog converter (DAC) array is employed, where the DAC injects currents or voltages to cancel out built-in offset voltages, allowing for adjustable cancellation range and resolution, and is compactly realized in modern CMOS processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If offset compensation is implemented using traditional methods, then offset voltage cancellation is achieved, but device complexity and area increase
Solution Approach 1:
The DAC array is designed to serve multiple functions: it acts as both the offset compensation mechanism and an integral part of the ADC structure. By reusing the same hardware resources for both conversion and offset cancellation, the patent avoids adding separate dedicated offset compensation circuits, thereby maintaining device simplicity while achieving accurate offset voltage cancellation.
Solution Approach 2:
The system uses its own internal DAC array to generate the compensation signal rather than requiring external offset compensation circuits. The DAC array leverages the existing digital control infrastructure of the ADC to automatically generate and apply offset compensation voltages, making the system self-sufficient and avoiding additional external components.
2Measurement precision
If a DAC array is used for offset compensation, then cancellation range and resolution are improved, but device area increases
Solution Approach 1:
The offset compensation function is divided into multiple discrete steps corresponding to different DAC array output levels. By segmenting the compensation range into manageable digital steps, the system achieves fine resolution without requiring a single large analog adjustment mechanism, allowing compact implementation through digital control of multiple smaller DAC elements.
Solution Approach 2:
The patent replaces traditional analog offset adjustment mechanisms with a digitally controlled DAC array. This substitution allows precise offset compensation through digital code words rather than mechanical or continuous analog adjustments, enabling compact integration of high-resolution compensation functionality within the ADC chip area.
3Reliability
If offset compensation circuitry is added to the ADC, then ADC operation accuracy is improved, but manufacturing complexity increases
Solution Approach 1:
The offset compensation functionality is merged with the existing ADC architecture by utilizing the same DAC array that is already part of the converter structure. This integration eliminates the need for separate offset compensation circuitry, reducing manufacturing complexity while maintaining improved ADC operation accuracy through the combined functionality.
Data Source
AI summary
An offset compensation scheme using a digital-to-analog converter (DAC) is disclosed. In some embodiments, a DAC is coupled to a circuit having an undesired current or voltage offset and is configured to at least in part compensate for the undesired current or voltage offset. For example, in some embodiments, the DAC injects current or voltage into the circuit that shifts a current or voltage of the circuit by an amount equal or similar in magnitude but opposite in polarity to a shift in the current or voltage of the circuit caused by the undesired current or voltage offset.